Method of Dissolving A Gaseous Hydrocarbon Into A Liquid Hydrocarbon

ABSTRACT

The present invention is directed to a method of dissolving a gaseous hydrocarbon into a liquid hydrocarbon to re-circulate gaseous components, which have separated from the liquid fuel mixture, back into the liquid fuel mixture, as well as, a method for making batch or continuous process amounts of mixed hydrocarbon fuels. The mixed hydrocarbon fuel is produced by introducing a volume of a liquid hydrocarbon into a vessel, and introducing a volume of a gaseous hydrocarbon into the vessel by bubbling the gaseous hydrocarbon into the liquid hydrocarbon at a gravitational low point of the vessel such that the bubbled gaseous hydrocarbon is dissolved into the liquid hydrocarbon to produce a liquid fuel solution. The vessel may be a mixing tank from which the liquid fuel is pumped into a vehicle fuel tank, or the vessel may be the vehicle fuel tank.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 10/973,007 filed onOct. 25, 2004, which claims the benefit of U.S. Provisional ApplicationSer. No. 60/514,392, filed Oct. 24, 2003. The entire contents of bothpatent applications are hereby expressly incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to methods of producing liquidfuel solutions, and more particularly, but not by way of limitation, toan improved method of dissolving a gaseous hydrocarbon into a liquidhydrocarbon to produce a liquid fuel mixture and to recirculate gaseouscomponents, which have separated from the liquid fuel mixture, back intothe liquid fuel mixture.

2. Brief Description of the Related Art

Most hydrocarbon fuels are composed of multiple hydrocarbons withvarying degrees of volatility. Even gasoline has a composite of severalhydrocarbons that vary between refineries and between locations toaccount for cold or hot conditions, or differences in altitude. Currentfuels may be stored and handled in liquid, liquid plus vapor, or vaporphases. The liquid phase of a liquid or liquid plus vapor mixture tendsto stratify or separate out with increasingly heavier componentsmigrating toward the bottom of the storage vessel when the fuel mixtureremains stationary over an extended period of time.

Examples of common fuels that have liquid plus vapor components arecommercial propane (LPG) and commercial liquid natural gas (LNG).Commercial propane contains propane, ethane, butanes, and otherhydrocarbons in a liquid plus vapor form due to the pressure at whichthese compounds are stored and handled (about 150 psig). Commercialliquid natural gas contains mostly methane in liquid plus vapor phase,with five percent or more of various heavier hydrocarbons containedmostly in the liquid parts of the fuel stored at cryogenic conditions(about −200° F.) in insulated tanks. Finally, commercial compressednatural gas (CNG) contains mostly methane with varying degrees of othercompounds, such as nitrogen or carbon dioxide, and is completelygaseous, thus remaining fairly well mixed.

Liquid and liquid plus vapor fuels have higher energy densities (energycontent per unit volume) than gaseous fuels. This allows the storage ofa greater quantity of useful energy in the fuel tank of a vehicle.However, the more volatile compounds, which are the lighter compoundssuch as methane, will tend to slowly leave the liquid mixture as a gasprimarily due to heat transfer into the fuel tank. If the fuel tankremains stationary for a long period of time, significant stratificationof the liquid combined with the vapor leaving the liquid tends to resultin the various liquid components to stratify with the heavier componentsmigrating to the bottom of the tank and the lighter components migratingtoward the top of the tank. This phenomena is commonly referred to as“weathering”. Weathering occurs for all mixed hydrocarbon fuels with aliquid phase under certain thermodynamic conditions which are specificto the composition of the particular fuel mixture. The problemsassociated with weathering have generally been overcome by reprocessingthe fuel. However, this requires significant handling of the fuel andthus significantly increases the production cost of the fuel.

To this end, a need exists for an improved method of dissolving agaseous hydrocarbon into a liquid hydrocarbon to re-circulate gaseouscomponents, which have separated from the liquid fuel mixture, back intothe liquid fuel mixture, as well as, a method for making batch orcontinuous process amounts of mixed hydrocarbon fuels. It is to suchmethods that the present invention is directed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a cross-sectional view of a mixing and storage tankconstructed in accordance with the present invention.

FIG. 2 is a cross-sectional view of a lower portion of a liquid inlettube looking left to right horizontally in FIG. 1.

FIG. 3 is a cross-sectional view of another embodiment of a mixing andstorage tank constructed in accordance with the present invention.

FIG. 4 is a schematic flow diagram of a process for manufacturing atwo-phase composite fuel within a vehicle storage tank.

FIG. 5 is a schematic flow diagram of another embodiment of a processfor manufacturing a two-phase composite fuel.

FIGS. 6A and 6B are a block diagram of a control algorithm for use inthe process of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

It has been found that a fuel composed of an approximately 50/50 massmixture of liquid petroleum gas (LPG) and compressed natural gas (CNG)offers a variety of advantages over other types of alternative fuels,such as vehicle mileage range while maintaining both economical andenvironmental superiority. The composite fuel has been shown to reducesome of the problems associated with the use of commercial compressednatural gas (CNG) or commercial liquid petroleum gas (LPG). For example,the fuel is stored at approximately half the pressure of CNG(approximately 1500 psig), but retains the high energy density of LPG.An example of a fuel composed of a 50/50 mass mixture of liquidpetroleum gas (LPG) and compressed natural gas (CNG) is disclosed inU.S. Pat. Nos. 5,900,515 and 6,111,154 issued to Mallinson et al., eachof which is hereby incorporated herein by reference. Preferably, the twophase fuel mixture comprises a gaseous methane and at least one otherhydrocarbon and a mole percent of methane from about 50 percent to about80 percent. The mixture of methane and the at least one otherhydrocarbon maintained at a temperature of about −1° C. or greater andat a pressure of about 8.0 Mpa or greater. As mentioned above, due tothe effects of weathering, problems are encountered when attempts aremade to store composite fuels.

Referring now to the drawings, and more particularly to FIG. 1, a vessel10 for mixing and storing a two phase fuel composite, such as in avehicle, in accordance with the present invention is illustrated. Thevessel 10 is an example of a standard natural gas storage vessel havinga single point of entry. However, double ended tanks may also be used.The vessel 10 is provided with an inlet tube 12, a liquid outlet tube14, and a vapor outlet tube 16. In a manner to be discussed in greaterdetail below, the composite fuel may either be mixed within the vessel10 or mixed outside the vessel 10 and then conveyed to the vessel 10. Ineither case, the gaseous fuel component is first introduced into thevessel 10 via the inlet tube 12 to raise the pressure in the vessel 10above the known vaporization pressure of the liquid fuel component. Whenthe composite fuel is mixed outside the vessel 10, the composite fuel isintroduced to the vessel through the inlet tube 12.

When the composite fuel is mixed in the vessel 10, the constituent fuelthat is normally liquid at the lowest pressure is then introduced intothe vessel 10 via the inlet tube 12. The more volatile, gaseous fuelcomponent is next introduced into the vessel 10 via the inlet tube 12.The inlet tube 12 has a lower portion 18 positioned near thegravitational low point of the vessel 10. The gaseous fuel component isslowly added by bubbling the gaseous fuel component into the liquid fuelcomponent. The bubbles are routed by the inlet tube 12 to the lowestgravitational point, and released downward through a series of openings20 (FIG. 2) oriented at angles just off straight downward (5 to 45degrees, depending on the downward velocity). This downward directionalrelease of the bubbles ensures that a dead layer of heavier hydrocarbondoes not become fixated in the tank (it is also possible to release thegas from the bottom wall upward, but the key is to avoid dead layers).The openings 20 of the inlet tube 12 should be sufficiently small (orpass to a device such as a porous block that does have sufficientlysmall orifices) to allow collapse of the bubbles rising from the inlettube 12 over the available length of liquid height above the inlet tube12.

The entire mixture is blended by bubbling until the pressure exists at apoint sufficiently over the critical pressure for the mixture toovercome pressure losses that might occur in handling the mix. Forexample, a 50/50 molar percent mix of methane and propane would be mixedto about 1350 psig at standard temperature conditions; a projectedultimate pressure for the mix would be to exceed 1265 psig. All bubblestend to collapse above the critical pressure, enforcing a uniformresultant mixture. The bubbling serves to avoid large deviation inadditional heavy hydrocarbon by avoiding unmixed regions in the tank.

If the mixture may be fully utilized at above the critical pressure ofthe mixture, then the feed from the vessel 10 should be located at thelowest gravitational point on the vessel 10. If the contents of thevessel 10 involves only pressures below the critical pressure, thenseveral extraction points may be needed. To this end, the extractiontube 14 is provided with a series of openings 22 extending along aportion of the extraction tube 14. The inlet tube 12 and the liquidoutlet tube 14 may be combined, although this may restrict the processtime and flow rate. Preferably, the extraction tube 14 extends to nearlytouch the bottom of the vessel 10.

As the vessel 10 is emptied by extracting liquid, vapor will be producedin the handling process. Some vapor may be utilized to maintain thenecessary pressure conditions in the vessel 10. Additionally, vapor maybe periodically captured by the vapor outlet tube 16 positioned atgravitationally high points in the vessel 10 and circulated back intothe vessel 10 by bubbling the vapor into the liquid via the inlet tube12 to maintain a uniform composition. Alternatively, the captured vapormay be metered to a vehicle engine (not shown).

FIG. 3 illustrates another embodiment of a vessel 10 a for mixing andstoring a two phase composite fuel in accordance with the presentinvention. The vessel 10 a is similar to the vessel 10 described abovewith the exception that the vessel 10 a has a horizontal configurationas opposed to a vertical configuration. The vessel 10 a is provided withan inlet tube 12 a, and a liquid outlet tube 14 a, and a vapor outlettube 16 a. The bubbles are routed by the inlet tube 12 a to the lowestgravitational point, and released downward at angles just off straightdownward (5 to 45 degrees, depending on the downward velocity). Thisdownward directional release of the bubbles ensures that a dead layer ofheavier hydrocarbon does not become fixated in the tank (it is alsopossible to release the gas from the bottom wall upward, but the key isto avoid dead layers).

The holes 20 a of the inlet tube 12 a direct flow downward and should besufficiently small (or pass to a device such as a porous block that doeshave sufficiently small orifices) to allow collapse of the bubblesrising from that tube over the available length of liquid height abovethe inlet tube 12 a.

As the vessel 10 a is emptied by extracting liquid, vapor will beproduced in the handling process. Some vapor may be utilized to maintainthe necessary pressure conditions in the vessel 10 a. This vapor may becaptured by the vapor outlet tube 16 a positioned at gravitationallyhigh points in the vessel 10 a. The captured vapor may then be fed backinto the vessel 10 a if captured at a high enough pressure or metered toa vehicle engine (not shown) if captured on board a vehicle at lowerpressure.

FIG. 4 is a schematic illustration of a process of making a mixedcomposite fuel within a vehicle fuel tank, such as the vessels 10 and 10a described above, in accordance with the present invention. Thisprocess depends on the thermodynamic end state required relative to themixed phase. The pressure associated with the usual state of individualconstituents does not match the end state of the mixed fuel. To use thecontents of vessels 10 or 10 a fully down to lowest pressure, thevolatile component of the mixture is first injected, if the tank/vesselpressure is lower than the thermodynamic vaporization point of theliquid constituent. Once the vaporization pressure of the liquid isreached, the constituent fuel that is normally liquid at the lowestpressure is first introduced into a sufficiently high pressure, ventedvessel, such as the vessels 10 and 10 a described above. The morevolatile, gaseous fuel is next introduced at the gravitational low pointof the vessel as described above. The more volatile fuel is usuallystored at higher pressure than the final mixture, thus simple mixing ofthe gas into the liquid is possible. Positive compression is only neededif the gaseous component is at a pressure less than or equal to thefinal required state (target pressure). As the higher pressure, gaseouscomponent is slowly added, the pressure is allowed to build up in themixture, until the final pressure that is required is met. Aftermanufacture of the mixture, re-circulation is then performedperiodically to maintain a uniform composition using the conceptsdescribed above.

Again, in order to use the contents of vessels 10 or 10 a fully down tolowest pressure, the volatile component of the mixture is firstinjected, if the tank/vessel pressure is lower than the thermodynamicvaporization point of the liquid constituent. Once the vaporizationpressure of the liquid is reached, the system then operates by firstpumping LPG, such as propane, into the vessel 10 from a storage tank 30via a liquid stream 32. Once the desired amount of LPG is pumped intothe vessel 10, CNG is allowed to flow from a storage tank 34 into thevessel 10 via a gas stream 36 bubbling through the LPG that is alreadydisposed in the vessel 10. By these means, the fuel is formulated onboard the vehicle. The desired amount varies depending on the size ofthe vessel 10.

The storage tanks 30 and 34 are located at a fueling site and areconstructed to be watertight to ensure maximum isolation. The storagetanks 30 and 34 are preferably enclosed in an insulated housing (notshown).

As shown in FIG. 4, the system includes a pump 38 and a compressor 39.The pump 38 is an 8 gpm Hydra-Cell D10 pump or other positivedisplacement pumping device similar to that shown and described inreference to FIG. 5, driven by an explosion proof motor 40. A pressurerelief loop 41 is installed to protect against over pressurization ofthe pump 38. A fill line 42 is provided with a coupling 43 forconnection with the vessel 10.

A controller (not shown) is used to monitor and control all functions ofthe system in a manner well known in the art. An example of a suitablecontroller is a Direct Logic 205 programmable logic computer (PLC). Thecontroller monitors a pair of axial turbine flow meters 45 and 46 orother precision flow devices, such as coriolis flow meters, and controlstwo valves 47 and 48, the pump 38, a pressure switch 50, and a pressuretransducer 52. The pressure switch 50 is used to indicate to thecontroller when the required pressure has been reached. The pressuretransducer 52 is used to keep track of the pressure in the CNG storagetank 34 in order to maintain correct flow meter calibration. The storagetanks 30 and 34 should be electrically isolated, and all wiring enclosedin rigid conduit and sealed junction boxes.

It has been found that fueling times are greatly reduced when thepressure in the vessel 10 is low (e.g., <100 psig). The fueling time hasbeen greatly reduced when this condition is present since the pump 38functions as a transfer pump. Also, the methane and propane content ofthe mixture is greatly enhanced due to turbulent convection masstransfer produced by the fast bubbling of CNG into the propane. Toimprove the speed of propane delivering to the vessel 10, the inletdownstream piping is preferably at least about 0.75 inches. The FIG. 4process is termed a “bubble-on-board” process because the mixed fuel isprocessed onboard a vehicle. This processing method may be suitable forlost fuel handling for small captive vehicle fleets or where theconstituent fuel compositions added to a vehicle are regulated.

FIG. 5 is a schematic illustration of a process for making and storing amixed two-phase composite fuel for fueling of a vehicle storage tankconstructed in accordance with the present invention. The processillustrated in FIG. 5 is termed a “fast-fill” process because theconstituent components are premixed, allowing for faster transfer to avehicle. The process also allows the filling of a vehicle that has anyresidual fuel onboard the vehicle, at any pressure within the design ofthe present invention. The process involves three primary steps: (1)pumping a liquid hydrocarbon, such as propane, from a storage tank 60into a mixing tank 62, (2) passing a gaseous hydrocarbon, such ascompressed natural gas, from a storage tank 64 into the mixing tank 62,and (3) pumping the composite fuel from the mixing tank 62 to a vehiclefuel tank 66. This is accomplished through a series of valves andsensors illustrated in FIG. 5. A secondary process is the identificationof the contents of the vehicle tank to be filled, after sufficientinventory of mixed fuel is available.

Propane, which is stored in the storage tank 60 at approximately 150psig, is conveyed from the propane storage tank 60 to the mixing tank 62with a pump 70. A 3-way valve 72 positioned upstream of the pump 70 anda 3-way valve 74 positioned downstream of the pump 70 cooperate todirect the propane to the mixing tank 62 along a conduit 76. Upstream ofthe valve 72, the propane is passed through a filter 78 to remove debrisand a flow meter 80.

The propane inlet of the mixing tank 62 is at the bottom of the mixingtank 62. The mixing tank 62 preferably is a tank that is rated for 5000psig. The mixing tank 62 is provided with an open loop 82 connecting atop cap 84 with a bottom cap 86. Pressure equalizes the liquid level inthe mixing tank 62 with the liquid level in the loop 82. A capacitivesensor 88 detects the liquid level of propane. The capacitive sensor 88is mounted outside the loop 82 at the maximum height of propane neededto prepare the composite fuel. When the liquid level reaches thepreselected height, the capacitive sensor 88 produces a signal whichcauses the valves 72 and 74 to close and operation of the pump 70 to beterminated. Subsequently, a 3-way valve 90 interposed in a conduit 92opens permitting compressed natural gas (CNG) to pass from the gasstorage tank 64 to the mixing tank 62.

The CNG, which is stored in the gas storage tank 64 at about 3000 psig,flows by regulated pressure (above the critical pressure as describedearlier) into the mixing tank 62. The 3-way valve 90 controls the flowof the CNG between a pre-filling conduit 94 and a mixing tank conduit96. The pre-filling conduit 94 permits the vehicle fuel tank 66 to bepre-filled with CNG before filling the vehicle fuel tank 66 with thecomposite fuel to avoid flash vaporization. The mixing tank conduit 96is connected to the top of the mixing tank 62 and is the bubbling linefor manufacturing the composite fuel. The mixing tank conduit 96 extendsinto the mixing tank 62 and down to near the gravitational low point ofthe mixing tank 62 for bubbling purposes in a manner similar to thatdescribed above in relation to the vessel 10. The CNG is passed througha flow meter 98 and bubbled into the mixing tank 62 until it reaches apressure above 1265 psig, at which time a pressure transducer 100produces a signal to close the valve 90 and thus terminate the flow ofgas from the CNG storage tank. The composite fuel in the mixing tank 62is now ready to be transferred to the vehicle fuel tank 66.

The vehicle fuel tank 66, when empty, has a much lower pressure than themixing tank 62. Therefore, to avoid flashing, the vehicle fuel tank 66is preferably pre-filled with CNG to a pressure near 1000 psig via thepre-filling conduit 94. A pressure transducer 101 located at the end ofthe pre-filling conduit 94 produces a signal to start and stop thepre-filling process.

With the vehicle fuel tank 66 pre-filled with CNG, the pump 70 isactuated and the valves 72 and 74 are operated to cause the compositefuel to pass from the mixing tank 62 via the conduit 76. The compositefuel then travels through a conduit 102, the valve 72, the pump 70, thevalve 74, and a conduit 104 and into the vehicle fuel tank 66. A flowmeter 106 measures the liquid volume of composite fuel delivered to thevehicle fuel tank 66. When the fuel capacity of the vehicle fuel tank 66is reached, a capacitive sensor 108 produces a signal to stop the pump70 and to close the valves 72 and 74.

For safety purposes, the process preferably includes a venting loop 110to prevent overfilling of the vehicle fuel tank 66. The venting loop 110includes a vapor extraction conduit 112 connectable to the vehicle fueltank 66 for capturing vapor and transferring the captured vapor into arecycle tank 114. The capacitive sensor 108 detects when the vehiclefuel tank 66 is full and overflows into the conduit 112 to the recycletank 114. The capacitive sensor 108 produces a signal to terminate thepump 70 and to close a valve 116 interposed in the conduit 112. Thecollected vapor in the recycle tank 114 may then be compressed andbubbled back into the mixing tank 62 via a conduit 118. a valve 119 isinterposed in the conduit 118 to control the flow of the vapor. Knowingthe target conditions of the thermodynamic mixture(pressure/temperature, which are unique at this design point), thisconstitutes the secondary sensing to reliably fill a partially fullvehicle tank with a nominal 50/50 molar mix of the composite fuel.

The mixing tank 62 should be rated for at least 3000 psi. meetingappropriate federal and state standards. The mixing tank 62 might eitherbe U-Stamped for 3000 psi, meet AMSE code for 3000 psi, or be made ofrated composite designed to the appropriate standard. The dimensions ofthe mixing tank 62 may be, by way of example, a length of about 74inches, an outer diameter of about 16 inches, and a volume of about 30US gallons (water volume). The mixing tank 62 is preferably a doubleended tank.

The pump 70 is preferably a hydraulic piston pump powered by a hydraulicpower assembly 120 and consists of a hydraulic cylinder 122 and a pumpcylinder 124. A suitable pump is commercially available from ParkerHannifin Corporation with the hydraulic cylinder 122 being model no. 2.5inches CJB2HKTV34AC10 (Parker or equivalent) and the pump cylinder beingmodel no. 3.25 inch JB2HKTV14A110/2 (Parker or equivalent). The examplehydraulic cylinder has a 2.50 inch bore, a cushioned head and cap, and a10 inch stroke. The pump cylinder has a 3.25 inch bore and 10.5 inchstroke. The pump operates using proximity sensors to signal when thecylinders should change direction. In production, larger cylinders andsteam/water/hydraulics/electrics or other driven engines might power thepumping process.

The valves and pump described herein are preferably controlled with aprogrammable logic controller. Control valves and controllersconstructed to operate in the manner described herein are well known inthe art. Thus, a detailed description of such components is not believednecessary to enable one skilled in the art to understand the operationof the system of the present invention. An example of a suitablecontroller is a Direct Logic 205 with a CPU 240 made by Koyo.

FIG. 6 shows a control algorithm for the process shown in FIG. 5. Thecontrol algorithm is written using ladder programming RLL Plus. Theprogram is composed of three main stages: filling propane into themixing tank 62, injecting CNG into the mixing tank 62 to a pressure of1500 psi, and transferring the mixture into the vehicle fuel tank.

From the above description it is clear that the present invention iswell adapted to carry out the objects and to attain the advantagesmentioned herein as well as those inherent in the invention. Whilepresently preferred embodiments of the invention have been described forpurposes of this disclosure, it will be understood that numerous changesmay be made which will readily suggest themselves to those skilled inthe art and which are accomplished within the spirit of the inventiondisclosed and as defined in the appended claims.

1. A method of mixing a two phase fuel mixture comprising a vaporcomponent and a liquid component in a vessel to reduce stratification ofthe fuel mixture, the method comprising: providing the two phase fuelmixture in the vessel, the two phase fuel mixture comprising a gaseousmethane and at least one other hydrocarbon and a mole percent of methanefrom about 50 percent to about 80 percent, the mixture of methane andthe at least one other hydrocarbon maintained at a temperature of about−1° C. or greater and at a pressure of about 8.0 Mpa or greaterwithdrawing at least a portion of the vapor component of the mixturefrom the vessel; and re-introducing the withdrawn vapor component intothe vessel by bubbling the withdrawn vapor component into the liquidcomponent of the fuel mixture at a gravitational low point of the vesselsuch that the bubbled vapor component is dissolved into the liquidcomponent and the fuel mixture is sufficiently agitated to effectivelymix the two phase fuel mixture.
 2. The method of claim 1 wherein thevapor component is bubbled into the liquid component of the fuel mixtureat a downward angle of from about 5 degrees to about 45 degrees relativeto a vertical axis of the vessel.
 3. A method of mixing a two phase fuelmixture comprising a vapor component and a liquid component in a vesselto reduce stratification of the fuel mixture, the method comprising thesteps of: providing the two phase fuel mixture in the vessel, the twophase fuel mixture comprising a gaseous methane and at least one otherhydrocarbon and a mole percent of methane from about 50 percent to about80 percent, the mixture of methane and the at least one otherhydrocarbon maintained at a temperature of about −1° C. or greater andat a pressure of about 8.0 Mpa or greater withdrawing at least a portionof the vapor component of the mixture from the vessel; andre-introducing the withdrawn vapor component into the vessel by bubblingthe withdrawn vapor component into the liquid component of the fuelmixture in a downward direction such that the bubbled vapor component isdissolved into the liquid component and the fuel mixture is sufficientlyagitated to effectively mix the two phase fuel mixture.
 4. The method ofclaim 3 wherein the vapor component is bubbled into the liquid componentof the fuel mixture at a downward angle of from about 5 degrees to about45 degrees relative to a vertical axis of the vessel.
 5. A method ofproducing a liquid fuel solution, the method comprising: introducing avolume of a liquid hydrocarbon into a fuel storage tank mounted on avehicle to provide fuel to the vehicle; and introducing a volume of agaseous hydrocarbon into the vessel by bubbling the gaseous hydrocarboninto the liquid hydrocarbon at a gravitational low point of the vesselsuch that the bubbled gaseous hydrocarbon is dissolved into the liquidhydrocarbon to produce a liquid fuel solution.
 6. The method of claim 5wherein the gaseous hydrocarbon is bubbled into the liquid hydrocarbonat a downward angle of from about 5 degrees to about 45 degrees relativeto a vertical axis of the fuel storage tank.
 7. The method of claim 5wherein the liquid hydrocarbon is propane and wherein the gaseoushydrocarbon is methane.
 8. A method of fueling a vehicle, the methodcomprising: introducing a volume of a liquid hydrocarbon into a mixingtank; and (a) introducing a volume of a gaseous hydrocarbon into themixing tank by bubbling the gaseous hydrocarbon into the liquidhydrocarbon at a gravitational low point of the vessel such that thebubbled gaseous hydrocarbon is dissolved into the liquid hydrocarbon toproduce a liquid fuel solution; (b) introducing a second volume of thegaseous hydrocarbon into a fuel storage tank mounted on a vehicle toprovide fuel to the vehicle; and (c) passing a volume of the liquid fuelsolution from the mixing tank and introducing the liquid fuel solutioninto the fuel storage tank.
 9. The method of claim 8 wherein the gaseoushydrocarbon is bubbled into the liquid hydrocarbon at a downward angleof from about 5 degrees to about 45 degrees relative to a vertical axisof the mixing tank.
 10. The method of claim 8 wherein the second volumeof gaseous hydrocarbon introduced into the fuel storage tank issufficient to pressurize the fuel storage tank to prevent flashvaporization of the liquid fuel solution upon the liquid fuel solutionbeing introduced into the fuel storage tank.
 11. The method of claim 10wherein the fuel storage tank is pressurized to about 1,000 psig by thesecond volume of gaseous hydrocarbon.
 12. The method of claim 8 whereinthe liquid hydrocarbon is propane and wherein the gaseous hydrocarbon ismethane.
 13. The method of claim 8 wherein the mixing tank includes anopen loop connecting a top of the mixing tank with a bottom of themixing tank and wherein the method further comprises: sensing the levelof the liquid hydrocarbon in the open loop to determine the level ofliquid hydrocarbon in the mixing tank.
 14. The method of claim 8 whereinsteps (a)-(c) are performed automatically.
 15. The method of claim 14further comprising using a ladder logic algorithm.
 16. The method ofclaim 8 wherein the liquid hydrocarbon and the liquid fuel solution areconveyed with a hydraulically driven piston pump.
 17. The method ofclaim 16 wherein the hydraulically driven piston pump is controlled by aprogrammable logic controller.
 18. The method of claim 8 furthercomprising: determining the amount of liquid fuel solution in thevehicle fuel tank prior to passing liquid fuel solution into the vehiclefuel tank.
 19. The method of claim 18 wherein the step of determiningthe amount of liquid fuel solution further comprises: venting a fixedvolume of vapor from the vehicle fuel tank; and measuring the pressureof the vented vapor.